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PubMed1987

Effect of head-neck position on elbow flexor muscle torque production.

The purpose of this study was to investigate whether the tonic neck reflex affects elbow flexor muscle torque production in healthy, young adults and which head-neck (H-N) positions have the greatest influence. Forty-eight male and female students between the ages of 18 and 35 years volunteered as subjects. Head-neck positions involving the sagittal and horizontal planes and combinations of these were tested. The nondominant hand was used to apply tension to the lever of an isokinetic analyzer under both isometric (static) and isotonic (dynamic) conditions. Peak torque was determined for each H-N position under each condition. Differences in peak torque were elicited more easily from the female subjects than from the male subjects. Head-neck rotation (horizontal plane) appeared to have a greater influence on elbow flexor muscle torque production than movements in the sagittal plane, particularly when movements in the two planes were combined. We concluded, therefore, that H-N position must be considered during rehabilitation of the upper extremity.

Adolescent↗

PubMed1992

Contribution of damped passive recoil to the measured shortening velocity of skinned rabbit and sheep muscle fibres.

Maximum shortening velocities of skinned fibres from rabbit psoas and sheep extensor digitorum longus muscles were measured by the slack test and by extrapolating force-velocity curves to zero load. Both overall muscle velocity and sarcomere velocity were measured with each method. Maximum sarcomere velocity measured by the slack test was not significantly different from that assessed from the force-velocity curves (p greater than 0.1). Maximum overall muscle velocity measured from the slack test was significantly (p greater than 0.001) and substantially (62% rabbit, 83% sheep) greater than maximum sarcomere velocity. The difference is attributed to damped recoil of the series elastic elements contributing to the overall muscle velocity. The extent and time course of this damped recoil in isotonic steps was assessed from comparisons of overall muscle length and sarcomere length records during isotonic steps. When the records were shifted and scaled so that they superposed during the late stages of isotonic shortening, there was a substantial difference between the early parts of the records. This difference was reduced by about half in association with the step and the remaining half declined at a diminishing rate following the step, lasting longer with lower loads. This result is explained by about half of the series elastic element behaving as a viscoelastic element and half being undamped. With steps to the lowest isotonic loads, which averaged 6.7% of isometric force in sheep and 9.5% in rabbit, the total series elastic element recoil (both damped and undamped) averaged 3.4% and 2.7% of fibre segment length, respectively, in sheep and rabbit. The rapid series elastic element recoil at zero load, assessed from the slack test, was approximately 50% higher, indicating a substantial series compliance at low forces. The contribution of an additional, longer lasting, damped series elastic element recoil to the overall muscle velocity can explain the greater maximum velocity that is frequently found with the slack test.

Animals↗

PubMed1999

Effects of load and tone on the mechanics of isolated human bronchial smooth muscle.

Isotonic and isometric properties of nine human bronchial smooth muscles were studied under various loading and tone conditions. Freshly dissected bronchial strips were electrically stimulated successively at baseline, after precontraction with 10(-7) M methacholine (MCh), and after relaxation with 10(-5) M albuterol (Alb). Resting tension, i.e., preload determining optimal initial length (Lo) at baseline, was held constant. Compared with baseline, MCh decreased muscle length to 93 +/- 1% Lo (P < 0.001) before any electrical stimulation, whereas Alb increased it to 111 +/- 3% Lo (P < 0.01). MCh significantly decreased maximum unloaded shortening velocity (0.045 +/- 0.007 vs. 0.059 +/- 0.007 Lo/s), maximal extent of muscle shortening (8.4 +/- 1.2 vs. 13.9 +/- 2.4% Lo), and peak isometric tension (6.1 +/- 0.8 vs. 7.2 +/- 1.0 mN/mm2). Alb restored all these contractile indexes to baseline values. These findings suggest that MCh reversibly increased the number of active actomyosin cross bridges under resting conditions, limiting further muscle shortening and active tension development. After the electrically induced contraction, muscles showed a transient phase of decrease in tension below preload. This decrease in tension was unaffected by afterload levels but was significantly increased by MCh and reduced by Alb. These findings suggest that the cross bridges activated before, but not during, the electrically elicited contraction may modulate the phase of decrease in tension below preload, reflecting the active part of resting tension.

Albuterol↗

PubMed1996

Isometric and isotonic muscle properties as determinants of work loop power output.

The power output of rabbit latissimus dorsi muscle was calculated under isotonic conditions and during oscillatory work. Isotonic shortening studies yielded a maximum power output of 120 W . kg-1 at a P/P0 of 0.4 compared to a maximum power output of 32 W . kg-1 obtained using the work loop technique. This difference can largely be explained by comparing actual work loops with those constructed using force velocity (P/V) and isometric data. At low cycle frequencies, work loop power output is quite close to that predicted from P/V and isometric data. However, at higher frequencies other dynamic muscle properties appear to exert a more marked effect.

Animals↗

PubMed1989

Do differences in innervation result in different post-synaptic responses to exogenous agonists?

1. The pharmacological reactivity of the epididymal and prostatic portions of the rat vas deferens to BaCl2, phenylephrine and carbachol were recorded by isometric and isotonic technique. 2. The maximum response induced by the three agonists were similar at the epidiymal end, while at the prostatic portion phenylephrine produced a response 80% lower than that of barium and carbachol. 3. The pD2 value to agonists and the sensitivity to calcium channel blockers were lower at the prostatic end. 4. The data suggest that not only the pharmacological reactivity of the prostatic and epididymal portions differs, but also that the activity of the prostatic portion is much more reduced to alpha 1-agonists.

Animals↗

PubMed1995

The effects of strength conditioning on older women's ability to perform daily tasks.

OBJECTIVES: The objectives of this study were to determine the effects of a strength-training program on walking speed and relative muscular stress, as measured by normalized integrated electromyographic (nIEMG) activity, while carrying a box of groceries and standing from a chair. DESIGN: Prospective intervention study. SETTING: Volunteer subjects from the community of Birmingham, Alabama. PARTICIPANTS: Fourteen healthy women aged 60 to 77 years. INTERVENTION: Sixteen weeks of total body strength conditioning. MEASUREMENTS: Before and after 16 weeks of strength conditioning, the following variables were evaluated for all subjects: (1) strength, six isotonic tests and two isometric tests; (2) walking velocity; (3) nIEMG of the biceps while carrying a box of groceries; and (4) nIEMG of the rectus femoris while standing from a chair. MAIN RESULTS: After the strength training program, subjects' isotonic strength increased significantly, an average of 52% on the isotonic tests and 31% on the isometric tests. Walking velocity also increased significantly (18%). nIEMG of the biceps decreased 36% while carrying a box of groceries. Rectus femoris nIEMG decreased 40% while standing and 47% while sitting. CONCLUSIONS: After strength conditioning, healthy older women showed not only substantially increased strength but also improvements in walking velocity and the ability to carry out daily tasks such as rising from a chair and carrying a box of groceries.

Activities of Daily Living↗

PubMed1994

Pulmonary arterial smooth muscle contractility in hypoxia-induced pulmonary hypertension.

The highly compliant low-resistance pulmonary vasculature is markedly altered with chronic hypoxia. Remodeling in response to hypoxia and/or hypertension involves hypertrophy and hyperplasia of smooth muscle and excessive deposition of connective tissue that likely contributes to the maintenance or exasperates the already elevated pulmonary arterial (PA) pressure. The purpose of this study was to investigate the effect of chronic hypoxia on the contractile properties of PA smooth muscle. Isometric and isotonic experiments were performed on excised PA rings from pulmonary hypertensive (induced by 14 days of hypoxia) Sprague-Dawley rats. A doubling of the vessel wall thickness occurred during the development of hypoxia-induced pulmonary hypertension. Functionally, there was a decrease in isometric stress (force to cross-sectional area ratio). No difference was detected in the velocity of shortening or in total shortening ability. This study provides evidence that, in addition to the morphological changes, changes in PA smooth muscle contractility also appear to play a role in the development and/or maintenance of hypoxia-induced pulmonary hypertension.

Animals↗

PubMed1984

The force-velocity relation of rat fast- and slow-twitch muscles examined at different temperatures.

The steady-state force-velocity relation was examined at temperatures between 35 and 10 degrees C in rat fast-twitch (extensor digitorum longus, e.d.l.) and slow-twitch (soleus) muscle preparations in vitro, with direct stimulation, and employing the isotonic release technique. The curvature of the force-velocity relation increased with cooling in both muscles; the increase was more pronounced below 25 degrees C. The maximum shortening velocity of e.d.l. muscle decreased with a Q10 (temperature coefficient) of 1.8 in cooling from 35 to 25 degrees C; it decreased with a Q10 of 2.4 in cooling below 20 degrees C. The shortening velocity of slow muscle was more temperature sensitive. The Q10 values for soleus muscle were 2.0 at 35-25 degrees C and 3.5 below 20 degrees C. The maximum rate of isometric tetanic tension rise had a temperature sensitivity similar to the maximum velocity of shortening in each muscle type.

Animals↗

PubMed1998

A kinematic theory of rapid human movements: Part III. Kinetic outcomes.

This paper describes the kinematic and kinetic properties of simple rapid movements using a single and unique framework based on a delta-lognormal law (Plamondon 1993a,b, 1995a,b). Predictions concerning isotonic measurements are made using the properties of acceleration profiles, as described by the first time derivative of the delta-lognormal law. Predictions dealing with isometric measurements are directly analyzed using the delta-lognormal law, after demonstrating the experimental equivalence between isometric forces and virtual velocity profiles. The theory is also used to make statistical predictions about the variability of numerous kinematic and kinetic variables. The overall approach can be viewed as if, at some level of representation, the central nervous system were planning, executing and evaluating simple rapid movements in terms of momentum and energy instead of forces. The unifying perspective provided by the theory constitutes a powerful tool with which to study and analyze movements under numerous experimental conditions, using a single analytical law.

Algorithms↗

PubMed1993

Shortening-length diagram: a new method of modeling skeletal muscle performance.

Muscle shortening is usually characterized in terms of force-velocity and length-active tension properties. We have examined a third relationship, that between shortening and initial length to further characterize muscle performance. This analysis shows that optimal shortening is achieved at a length (Ls) different from the length (Lo) of optimal tension development. Moreover, the analysis reveals discrepancies between results expected (using classical modeling) and experimental findings and these discrepancies increase with age. This effect of age on shortening has not been previously identified. Diaphragm muscle strips were dissected from male Fischer 344 rats of 3 and 24 months of age. Muscles were subjected, in vitro, to isotonic loads of either 30% or 50% of peak isometric tension (Po*) and shortened from initial lengths ranging from 80% to 130%Lo. The relationship between shortening and initial length was fitted by a second order polynomial using linear regression analysis. Results at 30% P/Po* indicate a difference in ability to shorten of 7% at Lo between muscles of young and elderly rats. The age-related change was enhanced under a load of 50% P/Po*, with a 46% difference in ability to shorten between young and old rats. The results show an age-related decrease in shortening of the diaphragm that is not predicted using classical muscle mechanics. Factors other than the length-tension relation and load must therefore be explored to explain decrements of shortening with age.

Aging↗

PubMed1993

[Effect of occupational physical work on blood pressure].

The present knowledge on blood pressure variability during occupational physical activity is based almost exclusively on the results obtained from the exercise tests, either isotonic (dynamic) or isometric (static). The findings of several studies indicate that during isotonic exercise in normotensive subjects the systolic blood pressure increases whereas the diastolic blood pressure shows only minor changes. In the hypertensives, both systolic and diastolic pressures tend to increase more substantially. Isometric exercise causes transient systemic hypertension but with individual differences. The exercise test reveal only transient values of systemic blood pressure and they are usually performed in a laboratory or at intervals during the workshift and after work. But still little is known how prolonged occupational physical work affects blood pressure and which of the work factors are involved. Ambulatory blood pressure monitoring, which makes it possible to obtain many readings a day also during normal working activity, seems to be an important new tool in the research into blood pressure variability. Certainly, it should be helpful in finding answers to some of the questions relating to that problem.

Blood Pressure↗

PubMed1992

Functional evaluation of the shoulder after transfer of the vascularized latissimus dorsi muscle.

The function of the shoulder after removal of the vascularized latissimus dorsi muscle in seventeen patients was compared with the function of the shoulder in seventeen control subjects. Physical examination of the extremity and instrumented muscle-testing were used to evaluate both the patients and the control subjects, and the patients also completed a questionnaire. Thirteen patients rated the appearance of the donor extremity as good, and sixteen patients perceived no functional impairment of the donor extremity. The range of motion of both shoulders was symmetrical in eleven patients and fourteen control subjects. Manual muscle-testing showed normal strength of the latissimus dorsi bilaterally in seven patients and in thirteen control subjects. Nineteen instrumented isometric, isotonic, and isokinetic tests were performed to assess the strength of each shoulder of all of the patients and control subjects, and the results in these two groups were then compared. there was no statistically significant difference in the strength of the two shoulders between the patients and the control subjects, with the exception that the patients exhibited weakness in the amount of isokinetic torque during extension of the shoulder with the limb in a position of 60 degrees of flexion and at a speed of 60 degrees per second. On the basis of these findings, and because of the inherent inaccuracy of manual muscle-testing, we concluded that transfer of the vascularized latissimus dorsi muscle had little effect on the range of motion, muscular strength, and function of the donor shoulder in our patients.

Adult↗

PubMed2002

Effect of partial outlet obstruction on rabbit urinary bladder smooth muscle function.

Bladder outlet obstruction secondary to benign prostate hyperplasia is associated with many cellular changes. This study was designed to determine whether these changes involve the contractile apparatus. Bladder smooth muscles from rabbits subjected to partial outlet obstruction for 2 wk were mounted for isometric force, isotonic shortening velocity, and myosin light chain (MLC) phosphorylation levels. Muscle strips from obstructed bladders exhibited spontaneous phasic activity; muscle strips from control bladders did not. Muscle strips from obstructed bladders exhibited increased sensitivity and higher levels of stress in response to the cumulative addition of KCl or carbachol compared with control. During noncumulative addition of KCl or carbachol, no differences in sensitivity were noted. Muscle strips from obstructed bladders had elevated basal MLC phosphorylation levels and stimulation produced small increases in MLC phosphorylation compared with control. V(max) during KCl stimulation of muscle strips from obstructed bladders was 10-fold lower than control. Our results suggest that bladder outlet obstruction produces a muscle cell that develops higher levels of force but with greatly reduced cross bridge cycling rates.

Animals↗

PubMed2002

Time course and magnitude of movement-related gating of tactile detection in humans. III. Effect of motor tasks.

This study investigated the relative importance of central and peripheral signals for movement-related gating by comparing the time course and magnitude of movement-related decreases in tactile detection during a reference motor task, active isotonic digit 2 (D2) abduction, with that seen during three test tasks: a comparison with active isometric D2 abduction (movement vs. no movement) evaluated the contribution of peripheral reafference generated by the movement to gating; a comparison with passive D2 abduction (motor command vs. no motor command; movement generated by an external agent) allowed us to evaluate the contribution of the central motor command to tactile gating; and finally, the inclusion of an active "no apparatus," or freehand, D2 abduction task allowed us to evaluate the potential contribution of incidental peripheral reafference generated by the position detecting apparatus to the results (apparatus vs. no apparatus). Weak electrical stimuli (2-ms pulse; intensity, 90% detected at rest) were applied to D2 at different delays before and after movement onset or electromyographic (EMG) activity onset. Significant time-dependent movement-related decreases in detection were obtained with all tasks. When the results obtained during the active isotonic movement task were compared with those obtained in the three test tasks, no significant differences in the functions describing detection performance over time were seen. The results obtained with the isometric D2 abduction task show that actual movement of a body part is not necessary to diminish detection of tactile stimuli in a manner similar to the decrease produced by isotonic, active movement. In the passive test task, the peak decrease in detection clearly preceded the onset of passive movement (by 38 ms) despite the lack of a motor command and, presumably, no movement-related peripheral reafference. A slightly but not significantly earlier decrease was obtained with active movement (49 ms before movement onset). Expectation of movement likely did not contribute to the results because stimulus detection during sham passive movement trials (subjects expected but did not receive a passive movement) was not different from performance at rest (no movement). The results obtained with passive movement are best explained by invoking backward masking of the test stimuli by movement-related reafference and demonstrate that movement-related reafference is sufficient to produce decreases in detection with a time course and amplitude not significantly different from that produced by active movement.

Adolescent↗

PubMed1994

Effects of prostaglandins E1 and E2 on cultured smooth muscle cells and strips of rat aorta.

Using patch-clamp and Indo-1AM techniques, we studied the effects of prostaglandins (PG) E1 and E2 on transmembrane ionic currents and cytosolic calcium concentration ([Ca2+]i) in cultured rat aortic smooth muscle cells (SMC) and on isotonic contraction-relaxation of strips of the rat thoracic aorta. In voltage-clamped at -70 mV single SMC PGE1 and PGE2 in concentration 100 nM evoked inward and outward currents. The inward current was unaffected by the Cl channel blocker DIDS (0.1 mM). The outward current was blocked by internal Cs+ and external Ba2+ and was likely due to increased Ca2+ activated K+ conductance. Application of PGE1 and PGE2 in the bath solution evoked relaxation of aortic strips in a concentration-dependent manner. In both cases indomethacin was ineffective. The rise in [Ca2]i evoked by PGEs was observed in single cells loaded with Indo-1AM. Whole-cell voltage-activated T- and L-type Ca2+ currents were reduced by both PGE1 and PGE2. The results obtained in this work indicate that in cultured rat aortic SMC PGE1 and PGE2 increase [Ca2+]i with subsequent activation of Ca(2+)-dependent K+ currents, block voltage-activated Ca2+ currents, and at the same time induce relaxation of aortic strips.

Alprostadil↗

PubMed1996

Potentiation of smooth muscle contractility after rapid changes in isotonic force.

The sudden application of step increases in afterload (0.4-3.0 s in duration) arrested the isotonic shortening of electrically stimulated ovarian ligament smooth muscle strips from rabbits. Force steps were chosen to produce, after initial rapid yielding, a quasi-steady state in which muscle length and force remained constant. Removal of the extra afterload allowed renewed shortening that began with a velocity transiently greater than that measured before the force step (at same muscle length). The rate of force redevelopment was also transiently potentiated under isometric conditions after the removal of the extra load. Both types of potentiation depended on force-step duration, and the transients decayed exponentially with a time constant of approximately 0.25 s. The stiffness of the muscle during the force step was initially depressed but then increased along an exponential time course while force and length remained constant. These observations are consistent with an initial detachment of a portion of the cross-bridge array, which then reattached during the course of the force step, with potentiation being due to either a transient increase in cycling rate or a time-dependent reconfiguration of cytoskeletal elements supporting the contractile system.

Animals↗

PubMed1986

Trunk flexion in healthy children aged 3 to 7 years.

I tested 80 male and 80 female subjects between the ages of 3 and 7 years on two exercises of isometric trunk flexor muscle strength (half-hold hooklying position and supine flexion position) and one exercise of isotonic trunk flexor muscle strength (hooklying sit-ups) to establish normative data for trunk flexor musculature capabilities. Measurements included the length of time the half-hold hooklying and supine flexion positions were maintained and the number of repetitions of sit-ups. I found no significant differences between the sexes in performance of the isometric tests. I did find, however, a significant difference between age groups for half-hold hooklying and supine flexion tests (p less than .0001), indicating that the ability to perform isometric trunk flexion improves with age. Height was another significant variable contributing to test results (p less than .0001). Children were able to perform sit-ups consistently at age 6 years only; the male subjects performed an average of 20 more sit-ups than the female subjects (p less than .04). I discuss in this article the possible contribution of neuromuscular maturation and physical growth to the development of normal trunk flexion. The results may be useful to clinicians to assess abnormal trunk flexion accurately in children aged 3 to 7 years.

Abdominal Muscles↗

PubMed1989

Effect of active pre-shortening on isometric and isotonic performance of single frog muscle fibres.

1. We studied the effects of shortening history on isometric force and isotonic velocity in single intact frog fibres. Fibres were isometrically tetanized. When force reached a plateau, shortening was imposed, after which the fibre was held isometric again. Isometric force after shortening could then be compared with controls in which no shortening had taken place. 2. Sarcomere length was measured simultaneously with two independent methods: a laser-diffraction method and a segment-length method that detects the distance between two markers attached to the surface of the fibre, about 800 microns apart. 3. The fibre was mounted between two servomotors. One was used to impose the load clamp while the other cancelled the translation that occurred during this load clamp. Thus, translation of the segment under investigation could be minimized. 4. Initial experiments were performed at the fibre level. We found that active preshortening reduced isometric force considerably, thereby confirming earlier work of others. Force reductions as large as 70% were observed. 5. Under conditions in which there were large effects of shortening at the fibre level, we measured sarcomere length changes in the central region of the fibre. These sarcomeres shortened much less than the fibre's average. In fact, when the load was high, these sarcomeres lengthened while the fibre as a whole shortened. Thus, while the fibre-length signal implied that sarcomeres might have shortened to some intermediate length, in reality some sarcomeres were much longer, others much shorter. 6. Experiments performed at the sarcomere level revealed that isometric force was unaffected by previous sarcomere shortening provided the shortening occurred against either a low load or over a short distance. However, if the work done during shortening was high, force after previous shortening was less than if sarcomeres had remained at the final length throughout contraction. The correlation between the force deficit and the work done during shortening was statistically significant (P = 0.0001). 7. Interrupting the tetanus for 0.5-3.0 s did not reverse the effects of shortening on isometric force; at least 5-10 min of rest were required before force recovered completely. 8. Sarcomeres accelerated during the period of shortening under constant load, indicating that the sarcomeres became progressively stronger. However, the acceleration was less than that predicted from the force-velocity relation applicable at each of the sarcomere lengths transversed during shortening. 9. Velocity of shortening appeared to be much more sensitive to previous shortening than isometric force. 10. Results obtained with the diffraction method were the same as those obtained with the segment method.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗